Support Extension Manager

[m3nu]

Description

There is now a handy frontend for managing extensions. It also works with this image, but installed extensions will disappear when updating or recreating the image because the extension is not added to /data/extensions/list.

I was wondering if there is any way to get around this. After looking at the related scripts in this repo, it seems the only way would be to have some hook in Extension Manager that appends the extension in /data/extensions/list. Maybe someone has a better idea?